Electrical systems for automobiles are becoming increasingly complex. Whereas the first automobiles had only simple lighting systems, today's vehicles can have well over a mile of wires connecting a myriad of devices to numerous microprocessors or electronic control units (ECU's). Thus, the electrical/electronic content of a modern automobile can exceed one third of the cost of the vehicle.
One reason for this proliferation of wires is that, traditionally, optional electronic functions are simply added onto a vehicle's basic electrical system. Thus, with each added function, additional wires are incorporated into the automobile. According to common current practice, each device typically has 2 or more dedicated wires connecting it to the ECU in charge of its functioning. Therefore, with the large number of electrically controlled devices found in modem automobiles, current ECU's have hundreds of wires connected to them. Each added wire brings the expense of the wire itself, and the expenses associated with the accompanying interconnections. A solution to this proliferation of wires is required.
As the volume of wires in automobiles increased, manufacturers began to rely on wiring harnesses in order to create manageable units for use in the manufacturing process. The earliest wiring harnesses were produced by bundling wires together with tape. Later, manufacturers began producing wiring harnesses made of molded semi-rigid or rigid corrugated plastic conduit or woven threading in order to protect the wiring from impact and other environmental conditions. Metal conduits have also been used as an alternative to hard plastics. Such harnesses are still in use today.
More recently, it has become possible to produce wiring harnesses out of synthetic materials which can be made soft or flexible in particular regions so as to aid in fitting the harness into the application, reduce vibrational noise, or to suit other such purposes. Such wiring harnesses are described in EPO Patent No. 0 288 752 B1.
One of the suggested solutions to the proliferation of wires has been the use of "smart" technology in the individual devices controlled by, or sending information to, the ECU. The use of smart technology in a device involves providing the device with the circuitry necessary to communicate with the ECU, and interpret and implement the commands provided by the ECU, and providing an ECU with suitable network capabilities, such as the multiplexing of device commands. By providing the device with a de-multiplexer, and using device-unique identifier information, commands may be multiplexed and sent from the ECU to various devices on the same cable, commonly known as a data link cable, with each device ignoring commands directed to other devices. Thus, the same data link cable can be used to serve multiple devices, and the amount of wiring required can be greatly reduced.
However, the incorporation of smart circuitry into each device is expensive. Smart circuitry typically consists of an analog/digital converter, a microprocessor, memory, a transceiver, a timing mechanism, often provided on a printed circuit board. These components and the boards themselves are expensive, particularly when the cost is multiplied over the number of devices which may be present in a modern automobile. For devices not already available in the market with smart circuitry, standard devices must be retooled and repackaged with smart circuitry, making this solution even less viable. Finally, in the case of engine systems, many devices are located in areas which are environmentally too severe to package electronics due to heat, vibration, and the presence of moisture.
Another suggested solution has been to provide smart electronics at points along the wiring system external to the wiring harnesses to handle the multiplexing functionality. This solution typically comprises providing electronic boxes spliced into the data link cable or involve incorporating smart electronics into already existing connectors. These additional boxes or connectors must be separately manufactured and incorporated into the wiring system, resulting in additional costs, interconnections, and failure points.